1. Field of the Invention
The present invention relates to a method and an apparatus for testing connections between terminals of semiconductor ICs (integrated circuits) and, more particularly, to a method and apparatus for testing connections between terminals of a plurality of semiconductor ICs mounted on a printed circuit board.
2. Description of the Related Art
Recent large scale integration (LSI) circuits have many terminals as well as connections that are formed between the terminals. As the number of terminal connections of LSI circuits increases, it becomes more difficult to test whether or not the LSI circuits are actually connected to one another through the terminals.
In television digital signal processing LSI circuits such as high-vision MUSE decoders, images will not be greatly affected if the lower one or two bits among, for example, 10-bit digital image data are incorrectly connected between terminals of the LSI circuits. In this case, a visual inspection of the displayed image is ineffective in checking for incorrect connections.
One method of testing connections between terminals of LSI circuits employs a board tester that supplies external test signals to a printed circuit board on which the LSI circuits to be tested are mounted. The test signals drive the LSI circuits, which provide resultant outputs. The resultant outputs are compared with reference values by a pattern comparator of the board tester, to thereby test the terminal connections of the LSI circuits.
Another test method arranges a test circuit inside an LSI circuit to be tested. The test circuit steadily provides a signal of a logic level, either HIGH or LOW, during a test period. The method determines whether or not connections of terminals of the LSI circuit are correct, depending on whether r not the LSI circuit correctly receives the signal.
According to the method of employing the board tester, a printed circuit board to be tested must have, in addition to original circuits, various test-related circuits such as a circuit for supplying test signals to the LSI circuits and a circuit for supplying output signals of the LSI circuits to the board tester that is external to the printed circuit board. These test-related circuits may deteriorate connection conditions, such as load capacitance between the terminals of LSI circuits, thus causing problems in high-speed digital signal processing circuits in particular.
The method of arranging a test circuit in an LSI circuit and steadily supplying a signal of a HIGH or a LOW level from the test circuit to the LSI circuit during a test period is incapable of testing high and low levels for a normal operation as well as dynamically changing AC characteristics.